Spatiotemporal dynamics of the cortex and their disruption in Shank3b mouse model of autism

Autism Spectrum Disorders (ASD) comprise a group of neurodevelopmental conditions characterized by behavioral and neuronal abnormalities. Phelan-McDermid Syndrome (PMS) is a specific neurodevelopmental disorder caused by deletions or mutations of the 22q13 region, which often encompass the SHANK3 gene. leading to ASD-like symptoms. Shank3-deficient mice are considered a reliable model for studying PMS, as they display autism-like behaviors and neural impairments. Optical techniques such as widefield fluorescence imaging (WFFI) and optogenetics are increasingly used to characterize and modulate abnormalities in ASD mouse models. In the first chapter of this thesis, we characterized the calcium indicators GCaMP7f and jRCaMP1b for large-scale monitoring of cortical activity. Using PHP.eB-mediated transfection, we achieved robust and widespread expression across the dorsal cortex, enabling longitudinal imaging. GCaMP7f was employed to study different anesthesia states, while jRCaMP1b was combined with the inhibitory actuator stGtACR2 to develop an all-optical approach for simultaneous inhibition and monitoring of cortical activity. Consistent with previous studies, a single light pulse elicited a rebound of activity, whereas a 1-second illumination at 0.82 mW significantly reduced resting-state activity. In the second chapter, we first characterized the behavior of Shank3b+/– mice, identifying altered anxiety-like and grooming behaviors. WFFI with GCaMP7f revealed age-dependent cortical hyperconnectivity compared to wild-type littermates, which was reversed under anesthesia. Using convolutional non-negative matrix factorization, we identified distinct spatiotemporal motifs underlying cortical activity. Motor and associative motifs were differently expressed between genotypes and contributed to the observed hyperconnectivity. Movement tracking during imaging further revealed that associative motifs were less correlated 1 second before movement onset in Shank3b+/– mice, suggesting impaired motor-predictive activity. In the third chapter, we investigated whisker-evoked cortical activity, observing disrupted sensory integration. Specifically, we found a reduced activated area, lower response amplitude in the barrelfield cortex, altered temporal adaptation, and more localized responses in Shank3b+/– mice. Finally, we explored transcranial direct current stimulation (tDCS) as a non-invasive neuromodulation strategy. Anodal tDCS (20 min) modulated cortical excitability, although effects were variable and not consistently genotype-dependent, suggesting further optimization of stimulation parameters. Overall, this work provides new insights into the developmental trajectory of cortical dysfunction in the Shank3b+/– model of ASD and highlights the relationship between altered network dynamics and behavioral impairments.